Genes hold secret of survival of Antarctic ‘antifreeze fish’

October 17th, 2008 - 1:24 pm ICT by IANS  

Washington, Oct 17 (IANS) Genes hold the secret of how and why some of the amazingly hardy fishes survive in the harshest of Antarctica’s icy waters.There are eight families of notothenioid fish, five of them inhabiting the Southern Ocean, the frigid sea that encircles the Antarctic continent.

These fish can withstand temperatures that would turn most fish to ice. Their ability to live in the cold - and oxygen-rich - extremes is so extraordinary that they make up more than 90 percent of the fish biomass of the Southern Ocean.

Dissostichus mawsoni, the Antarctic toothfish, is the largest of the notothenioid fish to inhabit the Southern Ocean.

University of Illinois (U of I) professor Arthur DeVries discovered in the late 1960s that some notothenioids manufacture their own “antifreeze proteins.” These proteins bind to ice crystals in the blood to prevent the fish from freezing.

In the new study, U of I professor C.H. Christina Cheng and her colleagues at the Chinese Academy of Sciences sought comprehensive genetic clues that would help explain how the Antarctic notothenioids survive.

“Nobody has ever actually looked at the whole range of biological functions in these fish that are important for living in this chronically cold environment,” Cheng said. “This is the first study that does that.”

Cheng and her colleagues wanted to know which genes were being translated into proteins at high levels in one representative species of Antarctic notothenioid, Dissostichus mawsoni, according to a U of I press release.

They analysed gene expression in four tissues: the brain, liver, head kidney, the primary blood-forming organ in fish and ovary of D. mawsoni.

“We saw this very peculiar profile where in each of these tissues the proteins that are highly expressed are from a small set of genes,” Cheng said. “Each tissue makes all kinds of transcripts - the genetic messages that are made into proteins - but we found that a small group of genes dominates the transcriptional process.”

The researchers reasoned that any proteins that gave the fish an advantage in a cold, oxygen-rich environment would be expressed at high levels in the Antarctic fish. But it could also be true that specific tissues simply expressed more of certain proteins.

The study appeared in the Proceedings of the National Academy of Sciences.

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